気体圧力下および真空下でのクラスレートハイドレート生成と分子ダイナミクス

抄録

  In this article, we review our recent neutron diffraction and quasi- and inelastic neutron scattering works on the following two water systems related to clathrate hydrates. The first one is the aqueous solutions prepared by applying high pressure of non-polar guest gas molecules. The second one is the amorphous solids prepared by depositing mixed gases of water and guest molecules on a cold substrate (10 K) under high vacuum. In the first system, the diffusion of water molecules became excessively slower below the formation temperature of gas hydrates and it depends on the amounts of solved guest molecules and formed hydrate crystals. In the second system, the intensity of low-energy excitation was reduced by increasing the hydrophobic interaction between the water and guest molecules. As increasing the temperature of the amorphous solids, the local cage structure grew up above the glass transition temperature (ca. 130 K) and finally hydrate crystals formed at 165 K. All of the above results indicate that the local structural fluctuation of hydrate cage occurs in the liquid or amorphous states in advance of the crystallization of clathrate hydrates.